ERYTHROMYCIN ESTOLATE
Clinical safety rating: safe
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
Erythromycin estolate is a macrolide antibiotic that reversibly binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by blocking the translocation step. It may also exhibit immunomodulatory and anti-inflammatory effects.
| Metabolism | Primarily metabolized in the liver via demethylation by cytochrome P450 3A4 (CYP3A4). Erythromycin estolate is also a potent inhibitor of CYP3A4, leading to significant drug interactions. |
| Excretion | Primarily hepatic via biliary excretion into feces; approximately 2-5% excreted unchanged in urine. <5% renal elimination. |
| Half-life | Approximately 1.5-2 hours in normal adults; prolonged to 5-6 hours in end-stage renal disease. |
| Protein binding | 90-95% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.6-0.9 L/kg; distributes well into tissues but not CSF. |
| Bioavailability | Oral: 35-45% (estolate form has higher absorption; food increases bioavailability). |
| Onset of Action | Oral: 1-2 hours (systemic absorption); peak serum concentrations at 4 hours. |
| Duration of Action | 8-12 hours for susceptible organisms following oral administration. |
| Molecular Weight | 1056.4 |
250-500 mg orally every 6-12 hours
| Dosage form | SUSPENSION |
| Renal impairment | No adjustment required for GFR >10 mL/min; for GFR <10 mL/min, reduce dose by 50% or extend interval to every 12-24 hours |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use due to increased risk of hepatotoxicity |
| Pediatric use | 30-50 mg/kg/day orally divided every 6-8 hours; maximum 2 g/day |
| Geriatric use | No specific dose adjustment; use with caution due to increased risk of QT prolongation and hearing loss, monitor renal function |
| 1st trimester | May cause acute hepatitis, especially in pregnant patients with a history of estolate hypersensitivity or hepatic dysfunction; generally avoid due to hepatotoxicity risk. |
| 2nd trimester | Limited data; consider alternative macrolides. Potential for maternal hepatotoxicity. |
| 3rd trimester | Avoid near term due to risk of infantile hypertrophic pyloric stenosis (IHPS) with erythromycin use in late pregnancy. |
Clinical note
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
| FDA category | Human |
| Placental transfer | Erythromycin estolate crosses the placenta; fetal serum levels are approximately 1-3% of maternal serum levels. Hepatic toxicity in mother may affect fetus. |
■ FDA Black Box Warning
WARNING: Hepatotoxicity – Erythromycin estolate has been associated with cholestatic hepatitis, which may be fatal. Avoid use in patients with hepatic impairment or history of liver disease. Discontinue immediately if signs of hepatic dysfunction (e.g., jaundice, elevated liver enzymes) occur.
| Common Effects | Nausea |
| Serious Effects |
Hypersensitivity to erythromycin or any macrolide antibioticPre-existing liver disease or hepatic dysfunction due to estolate-induced hepatitis riskConcomitant use with cisapride, pimozide, ergotamine, or dihydroergotamine (QT prolongation/ergot toxicity)Porphyria
| Precautions | Hepatotoxicity: May cause cholestatic hepatitis; avoid in patients with pre-existing liver disease., QT prolongation: Can prolong QT interval and increase risk of torsades de pointes; use caution with other QT-prolonging drugs or in patients with arrhythmias., Drug interactions: Potent CYP3A4 inhibitor; avoid concomitant use with statins, ergot alkaloids, certain benzodiazepines, and other drugs metabolized by CYP3A4., Myasthenia gravis: May exacerbate neuromuscular weakness., Allergic reactions: Including rash, urticaria, and anaphylaxis., Pseudomembranous colitis: Antibiotic-associated diarrhea and Clostridioides difficile infection., Ototoxicity: Reversible hearing loss, especially at high doses or with renal impairment. |
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| Breastfeeding |
| Excreted into breast milk in small amounts, but considered compatible with breastfeeding. May increase risk of infantile hypertrophic pyloric stenosis (IHPS) in neonates exposed via milk. |
| Lactation Rating | L2 (Possibly safe; caution in infants <6 weeks due to IHPS risk) |
| Teratogenic Risk | First trimester: No increased risk of major malformations based on large cohort studies. Second and third trimesters: Use associated with increased risk of infantile hypertrophic pyloric stenosis (IHPS) when used after 32 weeks gestation. Overall FDA Category B. No evidence of fetotoxicity or teratogenicity in animal studies. |
| Fetal Monitoring | Monitor liver function tests due to risk of cholestatic hepatitis (especially with estolate salt). Monitor for signs of infantile hypertrophic pyloric stenosis in neonates exposed after 32 weeks gestation: projectile vomiting, visible peristalsis. No routine fetal monitoring required otherwise. |
| Fertility Effects | No evidence of adverse effects on fertility in animal or human studies. Reversible impairment of sperm motility reported in vitro at high concentrations but clinical significance unknown. |
| Food/Dietary | Take erythromycin estolate on an empty stomach. Avoid grapefruit juice as it inhibits CYP3A4 and may increase drug levels and toxicity. High-fat meals may delay absorption; maintain consistent timing relative to meals. |
| Clinical Pearls | Erythromycin estolate is contraindicated in patients with pre-existing liver disease or hepatic impairment due to risk of hepatotoxicity. It is a cytochrome P450 3A4 inhibitor and can increase levels of statins, warfarin, and other CYP3A4 substrates. Use with caution in patients with myasthenia gravis as it may exacerbate weakness. It is not recommended for use during pregnancy (category B) but is preferred in children for its palatable suspension. Monitor for QT prolongation in at-risk patients. |
| Patient Advice | Take this medication on an empty stomach, at least 1 hour before or 2 hours after a meal, to maximize absorption. · Do not take with grapefruit juice as it may increase side effects. · Complete the full course of therapy even if you feel better to prevent resistance. · Avoid alcohol while taking this medication as it may increase liver toxicity risk. · Report any signs of liver problems: yellowing of skin or eyes, dark urine, severe stomach pain, or persistent nausea/vomiting. · Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding. · This medication may interact with blood thinners, statins, and certain heart medications; provide a full list of your medications to your doctor. |